This invention relates to packaging materials and in particular, though not solely, to embossed sheet material used in packaging heavy loads such as large metal coils or rolls or stacks of rectangular cut sheet metal.
In order to avoid or minimise damage to heavy loads such as cold rolled steel coils during transportation and storage, specialised packaging solutions are required. In the case of steel coils, the extreme weight (up to around 20 tonnes) over a surface contact area as small as 0.5 m2 makes it difficult to meet the desirable requirement of maintaining separation between the ground and the steel to avoid corrosion during storage. The packaging material should also be puncture resistant, have a high impact strength and resistance to compression under the weight of a coil. It would also be beneficial for the packaging material to be recyclable, cheap to produce and manageable (light weight and easily worked into position around a coil).
Currently, there are a number of alternative materials used in packaging steel coils. Some manufacturers package their steel coils in steel or hard fibre hardboard, usually held together with steel straps. The steel coil may be (but is not always) shipped on a wooden pallet either with the axis of the coil vertical or horizontal. Some steel coils are wrapped in sheets of paper, such as kraft paper, plastics stretch wrap or a tear resistant plastic material (such as polyethylene or polypropylene) having one or more layers, sometimes with at least one layer being impregnated with a corrosion inhibitor (see for example U.S. Pat. No. 5,983,598). However these materials offer insufficient protection and padding beneath the steel. Laminated polyethylene/polypropylene (see for example U.S. Pat. No. 5,928,770) has also been suggested as a packaging material for steel coils however the manufacturing costs for this material would be prohibitive.
It is therefore an object of the present invention to provide a protective packaging sheet which goes at least some way towards overcoming the above disadvantages.
Accordingly, in a first aspect, the invention consists in a protective packaging sheet comprising:
front and rear surfaces, at least one of the surfaces having a repeating pattern therein,
the repeating pattern consisting of shaped protuberances juxtaposed with adjacent shaped protuberances to provide a gap around each shaped protuberance, the shaped protuberances extending from the at least one of the surfaces and being positioned in such a way that all straight lines projected onto said surface of the sheet cut through the shaped protuberances in addition to the gaps.
Preferably the protective packaging sheet is embossed to provide the shaped protuberances.
Preferably the front and rear surfaces both include a repeating pattern with the rear surface pattern being the inverse of the front surface pattern.
Preferably the contact surface area of the front surface is substantially equal to the contact surface area of the rear surface.
Preferably the packaging sheet has three levels, the front surface, the rear surface and a middle level between the front and rear surfaces, the middle level comprising a surface of connecting webs connecting adjacent shaped protuberances.
Preferably some of the connecting webs extend in a direction lateral to the shaped protuberances and others extend in a direction substantially perpendicular to the lateral direction.
Preferably the shaped protuberances are substantially tessellatable.
Preferably the shaped protuberances are xe2x80x9cTxe2x80x9d shaped in plan.
Preferably the packaging sheet is formed from a flat sheet of thermoplastics material wherein the distance between the front and rear surfaces of the packaging sheet is less than or equal to about 5 times the thickness of the thermoplastics sheet from which it is formed.
Preferably the gaps between the shaped protuberances are filled with insulating foam.
Preferably a thin sheet is laminated to the furthermost projecting sections of either or both of the front and rear surfaces.
Preferably the shaped protuberances comprise a top surface protruding from the packaging sheet atop side walls which are rounded, bevelled or sloped relative to a direction perpendicular to the plane of the packaging sheet.